The invention relates to a dishwasher with a sorption drying device. The invention further relates to a method for operating a dishwasher with at least one partial step “drying”, in which air from a washing container of the dishwasher and/or ambient air is in this partial program step directed through a sorption column with reversibly dehydratable material into the washing container by a fan, and humidity is removed from the air when the same is directed therethrough.
Conventional dishwashers have, as is well known, a washing process whose programmed sequence consists of at least one partial program step “pre-wash”, a partial program step “cleaning”, at least one partial program step “clear washing and a partial program step “drying”. To increase the cleaning effect, the washing bleach is in this case heated before or during a partial program step. The washing bleach is normally heated by electrical heating devices. Different drying systems are known for drying the items to be washed in a dishwasher.
For example, DE 20 16 831 discloses a dishwasher of the type already mentioned, in which the air is directed from the washing container through a sealable opening in the wall of the washing container on reversibly dehydratable material, and from there out trough an opening. The desorption of the reversibly dehydratable material takes place during the stationary phase of the appliance, the water vapour formed thereby being directed out through the opening. The dishwasher described is disadvantageous from the energy viewpoint because the regeneration of the reversibly dehydratable material takes place during a stationary phase of the appliance and therefore at a time when none of the partial program steps described above is being carried out. A further disadvantage consists in the fact that damage to the surrounding kitchen furniture by the discharge of the water vapour formed during the regeneration of the reversibly dehydratable material to the outside cannot be ruled out. Here the regeneration is associated with an additional energy requirement which is added to the energy required during the partial program steps.
In order to minimise the energy expenditure when a dishwasher is operated, a dishwasher with a washing container and devices for washing cutlery and dishes by means of a washing bleach is known from DE 103 53 774.0 of the applicant, which dishwasher has a sorption column connected in an air conducting manner to the washing container and containing reversibly dehydratable material, where on the one hand the sorption column is for drying the cutlery and dishes and on the other hand the thermal energy introduced for desorption of the sorption column is used to heat at least partially the washing bleach and/or the cutlery and dishes in the washing container.
To solve the same problem DE 103 53 775.9 of the applicant proposes guiding air from a washing container and/or from ambient air through a sorption column and into the washing container for operating an appliance in the at least one partial program step “drying”, the sorption column containing reversibly dehydratable material and removing humidity from the air when it is directed through it.
Because of the use of reversibly dehydratable material with a hygroscopic property, e.g. zeolith, heating of the items to be treated is no longer normally necessary in the partial program step preceding the partial program step “drying”. This allows a considerable saving in energy.
EP 0 358 279 B1 discloses a device for drying cutlery and dishes in a domestic dishwasher in which the washing bleach is heated by a heater arranged outside the washing container, preferably an electric geyser, a largely closed drying system being provided in which air circulates from the washing container via a drying device that can be regenerated by heating and from this back into the washing container. In this case the drying device consists of a drying container in thermal contact with the heater, which container is filled with a drying agent adsorbing the humidity. The connection of the drying container to the heater that is provided in any case for heating the washing bleach means that the drying device is operational immediately after the washing process. Here the drying agent is applied at least partially as a jacket around the heating elements of the heater so that the drying agent can be heated in the drying container during each heating process and can therefore be dried.
The drying container is designed as a double-walled hollow cylinder in which the drying material is stored. The inlet and outlet opening for connection to the closed air system is arranged in a diagonally opposing configuration. The disadvantage of this is a relatively high flow resistance, with the result that the fan provided for promoting the air flow must be operated at very high power. This has a negative effect on noise development and energy consumption.
Because of the structural design of the sorption drying device, which requires inhomogeneous introduction of heat into the drying material, the desorption is time consuming and may also result in local overheating of the drying agent and hence irreversible damage. Desorption is also difficult because the heater is arranged in the centre of the double-walled hollow cylinder and radial propagation of the heat to the drying agent located close to the outer hollow cylinder wall is hardly possible due to the air flowing axially past it.